The present invention relates to a process for manufacturing TFT liquid crystal displays and, more specifically, to a process for manufacturing pixel electrodes with slant diffusers for serving as the reflection members of TFT-LCD devices.
With the advance of techniques for manufacturing thin-film transistors, the liquid crystal displays (LCD) are widely applied in electrical products, such as PDAs, laptops, cellphones, high resolution television sets, etc. due to advantages as smaller size, portability, and lower power consumption. Particularly the up-to-date reflective LCD device is usually performed by utilizing the reflection of light incident from outside, wherein the pixel electrodes made of metal materials are applied to serve as reflection members. Thus the light reflected form the pixel electrodes performs desired images on the displays through liquid crystal molecules and color filters. The reflective type liquid crystal display that does not require a backlight has been vigorously developed because this type of displays is power saving, thin and lightweight. In addition, since members for the backlight are not necessary, the cost may be reduced.
Notedly, the deeply concerned and important key point is how to promote efficiency of light reflection because the light source of the reflective type LCD comes from the external illumination. In prior art, polarizing plates are introduced to adjust the phases of incident lights for increasing reflection intensity. However, it is not practical to apply the additional polarizing plates into the reflective type LCD. Another solution is to fabricate the pixel electrodes with rough surface for serving as the reflection diffusers for completely utilizing external illuminations, promoting efficiency of reflections and increasing contrasts.
Please refer to FIG. 1, the cross-sectional view of TFT-LCD with rough reflection fabricated by prior art is shown. The related process comprises follow steps. A gate structure 12 is defined on a glass substrate 10 first. Then an insulating layer 14 is deposited on surfaces of the gate structure 12. A semiconductor layer 16 such as amorphous silicon, a doped silicon layer 18 and a metal layer are sequentially formed on the gate structure 12. Next a photolithography procedure is performed to define a drain structure 20 and a source structure 22. After the TFT-LCD 24 is fabricated, an additional step is performed to form plural bumps 26 made of photoresists in the areas where applied to define pixel electrodes. Next a passivation layer 28 such as polymer material is coated on the bumps 26. And a pixel electrode 30 is formed above those layers. Thus, the reflection efficiency can be promoted due to the pixel electrode 30 having a rough and uneven surface.
However, for forming the bumps 26, it is necessary to deposit a photoresist layer on the glass substrate 10 first and perform the lithography, developing, and baking steps for defining bump patterns. It is required to fabricate an additional reticle applied to the above procedures. Therefore the cycle time is prolonged and the throughput is reduced cause the additional photomask and related lithography steps.
Besides, though the bumps 26 shown in FIG. 1 can be applied to increase the light receiving efficiency of the reflection member from outside illuminations. The brightness is still limited cause that the angles and ranges of reflected lights from the diffusers are not regulated and normalized. Accordingly how to manufacture the TFT-LCD devices with rough electrodes without the additional reticle and how to gather up the reflected lights within the possible view angles for users are the most important issues nowadays.
The first objective of the present invention is to provide a method for manufacturing a TFT-LCD device having pixel electrodes with rough surfaces for increasing the intensity of reflected lights.
The second objective of the present invention is to provide a method of forming pixel electrodes with the required angles of reflection wherein plural ridge bumps are defined to make the most outside illuminations can be reflected along the predetermined angles.
The third objective of the present invention is to provide a method of defining pixel electrodes with slant and rough surface for serving as diffusers.
A method of forming a TFT-LCD device with a slant pixel electrode for serving as the diffuser member is disclosed. In the first embodiment, the method comprises the following steps. First, a first metal layer is formed on a substrate. And a first etching procedure is done to etch the first metal layer for defining a gate structure. Notedly, the halftone reticle and slit reticle can be applied to define the slant photoresist patterns for defining plural ridge bumps of first metal layer simultaneously when the gate structure is defined. Each the ridge bump has a first bevel and a second bevel. Next a first insulating layer is formed on the gate structure, the plural ridge bumps and the substrate wherein the first insulating layer along the first bevel has a first inclined plane and along the second bevel has a second inclined plane. Then a semiconductor layer is formed on the first insulating layer above the gate structure to serve as channels. And a second insulating layer is deposited and etched by a second etching procedure to define an etching stopper above the gate structure. Subsequently a second metal layer is formed thereon and a third etching procedure is done then to etch the second metal layer to define drain/source structures aside the etching stopper. Next a passivation layer is formed on the drain/source structures and the first insulating layer, wherein the passivation layer is etched to expose a portion of the drain/source structures. A pixel electrode is then formed on the passivation layer.
In the second embodiment of the present invention, plural insulating protrusions are defined on the ridge bumps simultaneously when the second etching procedure is performed to etch the second insulating layer wherein the insulating protrusions are distributed along the first inclined plane of the first insulating layer. Thus the pixel electrode deposited latter can duplicate the shapes of the ridge bumps and protrusions to form the rough and uneven diffusers.
Similarly in the third embodiment, plural metal protrusions are defined above the ridge bumps when the third etching procedure is performed to etch the second metal layer simultaneously wherein the metal protrusions are distributed along the first inclined plane. Thus the pixel electrode with the rough and uneven diffusers can be served as the diffuser members.
And in the fourth embodiment, the metal protrusions and the insulating protrusions are both fabricated on the first inclined plane for highly concentrated roughness. Of cause these protrusions can also be applied along both the first and second inclined plane to promote the reflection efficiency.